178 PEOr. "W. K. PABKER ON THE STETJCTUEE AND 



is about equal in size to the pharyngo-hyal ; this segment possibly corresponds to the 

 distinct symplectic of the Sturgeon and Paddle-fish^. 



The lower part of the hyoid arch is longer and broader than the large mandibular 

 ramus (PI. XXXVI. fig. 2, c.hy) ; its lower part is broken up into three small segments, 

 equalling in average size the upper elements. 



This broad but solid rib of cartilage is arcuate ; in general form it is narrower above, 

 and broader below, the top part {st.li) being both notched and rounded ; the broad lower 

 part is emarginate, and has two lateral facets for the hypohyals {h.hy). 



There are two hypohyals {h.hf, hJif) attached to the supero-external angle of the 

 great cornu ; but these have become confluent (see in Menojjoma, PL XXXIX.) ; 

 together they form a thickish rod hooked inwards to join the median piece {h.hy), which 

 has coalesced right and left with these small distal hypohyals (Pl.XXXVlI. fig. 4, h.hy'). 



Tlie third hypohyal (h.hy^) is a truncated oval, attached by its broad part to the 

 infero-internal angle of the great cornu (c.hy). 



Outside the largest hypohyal there is another very small nucleus of cartilage on the 

 left side. 



The ligaments connecting the parts at the angle of the mouth are well seen iu this 

 skull. The " suspensorio-stapedial ligament " has the pliaryngo-hyal in its substance, 

 and the " hyo-suspensorial " (h. s.l) has the epihyal (e.hy) in its upper end ; the " mandi- 

 bulo-hyal" (m. h.l) runs upwards and backwards under the distal part of that ligament 

 from the angle of the jaw, and is attached nearer the end of the styloid part of the 

 ceratohyal. 



In Menohranchus none of these ligaments have cartilage in their substance. 



The basihyal {h.hy), contrary to rule, sends a process backward towards the first basi- 

 branchial ; it is pyriform, with tlie narrow end behind, and is confluent right and left 

 with the small second hypohyals. 



The third and fourth branchial arches are not retained in this species ; they are in 

 Menopoma, and also in a small Japanese " Cryptobranch," viz. Onychodactylus (Trans. 

 Linn. Soc. ser. 2, Zool. vol. ii. 1880, pi. xix.). 



The next basal element is roughly marked out into a first and second segment 

 (PI. XXXVII. fig. 3, b.hr) ; it is a roughly orbicular plate of cartilage notched in front 

 and on each side ; and the left side is the larger of the two. 



The first branchial arch has lost its upper element ; there is only an unossified cerato- 

 branchial {c.hr^), an arcuate, solid, thickish rod, hooked inwards above. 



The second arch is one fourth larger; but it has two parts — an epi- and a cerato- 

 branchial {c.hr, e.hr), marked out by extensive ossification ; as phalangiform bony bars, 

 united by cartilage ; the upper segment is a little less than the lower. 



Becajntulation of the Cranial Elements of Sieboldia, and Comparison with Menopoma. 

 As the description of the skull of Menopoma comes next, and as these two skulls 



' I am not sure that the segment hero caDed " epihyal " does not answer to the " interhyal " of Fishes ; 

 if so. then the styloid end of the " ccrato-hyal " would be the non-segmented " epihyal." 



